Right-click and save as (lots O options!):

Best Quality - Full-size (720x480):
Demo Reel - Quicktime H.264 (21mb)(only if you have Quicktime 7)
Demo Reel - Divx avi (25.7mb)(DIVX 6 or higher)

Medium Quality - Medium-size (540x360):
Demo Reel - mpeg1 (34.5mb)(when in doubt, mpeg1 will work on Windows)
Demo Reel - Quicktime Sorenson3 (47.9mb)

Demo Reel Breakdown pdf